Genomic structure of phage F22, a hybrid between serologically and morphologically unrelated Salmonella typhimurium bacteriophages P22 and Fels 2

Abstract

Salmonella typhimurium phage P22 can recombine with a serologically and morphologically unrelated Salmonella phage Fels 2 to yield the hybrid phage F22 at a frequency of about 10−12. F22 has inherited the entire late genes (protein coat and tail structural genes) of Fels 2 but carries some P22 early genes. P22 genes in the F22 phage were indentified by marker rescue of various P22 mutants. The F22 genome carries the x-erf-c-18-12 segment of the P22 genome. A number of P22 amber mutants were also tested to support these data. The F22 region homologous to P22 was mapped by scoring the ratio of P22 backcross recombinant types in lysates of F22 lysogens superinfected with P22c2ts12. The ratio of the distances between these markers and the ends of the homologous region was determined. Furthermore a new F22 hybrid designated F22dis, containing both P22 immunity regions (c and Im), was isolated at a frequency of about 10−4 by superinfecting F22 lysogens with P22. F22dis phage has lost some Fels 2 gene(s) which have been replaced by the P22 segment containing the Im region, resulting in formation of a defective hybrid phage. © 1986, Cambridge University Press. All rights reserved.